And Alkaline Earth Metals Research Articles

Density Functional Theory Study on Na+ and K+ Catalysis in the Transformation of Glucose to Fructose and HMF in Hydrothermal Environments

Hydrothermal carbonization (HTC) is an efficient method for converting biomass into biochar. Hydrochar contains catalytic components such as alkali and alkaline earth metals (AAEMs); however, the mechanisms by which highly active metals such as potassium (K) and sodium (Na) catalyze the conversion of small carbon–water compounds into hydrochar in hydrothermal environments remain unclear. In this study, glucose was used as a small molecule model, and Na+ and K+ were used as catalysts to investigate the catalytic reaction mechanism during the hydrothermal process using density functional theory (DFT). In the presence of different ions at various binding sites, glucose isomerizes into fructose, which subsequently undergoes three consecutive dehydration reactions to form 5-hydroxymethylfurfural (HMF). The results indicate that the catalytic effectiveness of Na+ and K+ in the isomerization of glucose to fructose is optimal when interacting with specific oxygen sites on glucose. For Na+, the interaction with the O1 and O2 oxygens provides the lowest reaction barrier of 37.16 kcal/mol. For K+, the most effective interactions are with the O3 and O4 oxygens and the O5 and O6 oxygens, resulting in reduced reaction barriers of 54.35 and 31.50 kcal/mol, respectively. Dehydration of fructose to HMF catalyzed by Na+ ions, the catalytic effectiveness at different positions is ranked as O5O6 > O1O5, whereas for K+, the ranking is O1O5 > O5O6. This study explores the catalytic effects of Na+ and K+ at different binding sites on the hydrothermal reactions of glucose at the atomic level, offering theoretical support for designing catalysts for the HTC of sludge.

Study on the behavior of AAEMs removal and the evolution of microscopic characteristics in high alkali coal under different acids

ABSTRACT In this paper, the removal behavior of alkali and alkaline earth metals (AAEMs) and the evolution of microscopic characteristics in high alkali coal under the leaching of inorganic and organic acids are studied. The results show inorganic acids have better effect on the removal of AAEMs because of their stronger ability to convert carboxylate and phenol salts into covalent carboxylic acids and phenols. Citric acid has a slightly weaker effect than inorganic acids, and oxalic acid has the least effect. The improvement of slagging characteristics is consistent with the removal ability. Sulfuric acid, hydrochloric acid and citric acid are more effective in enhancing the calorific value of coal, with an enhancement of about 0.60 MJ/kg. After leaching, the pores and cracks in the coal are developed, and the mesopores have a tendency to shift to a lower pore size range. This trend is most pronounced in citric acid leached coal and hydrochloric acid leached coal. Sulfuric acid seriously damage the surface morphology, which results in a tendency of large pore transfer in S-form coal.

Straw-based biochar prepared from multi-step KOH activation and its structure-effect relationship of CO2 capture under atmospheric/pressurized conditions via experimental analysis and MD/DFT calculations

Porous carbon-based CO2 capture holds great promise. However, the preparation process, pore structure and oxygen/nitrogen functional groups of porous carbon on CO2 adsorption still remain unclear. Herein, we develope straw-based biochar with ultra-high specific surface area(SSA), high micropore ratio and different O/N content by modifying the two-step KOH activation procedure and confirm the KOH activation mechanism, CO2 adsorption characteristics, and the structure-effect relationship of CO2 capture. The KOH activation process is controlled by the activation temperature and is divided into five temperature zones. The pickling treatment enhanced the activation effect of biochar, with a SSA of 3567.33 m2/g and a microporous ratio of 96.05 %. The potassium-containing active components reacts with the defective carbon structure above 800 °C catalyzed by alkali and alkaline earth metals(AAEMs), but reacts with the aliphatic hydrocarbon group after pickling. H-4–9-4-m has a maximum CO2 adsorption capacity of 24.77 mmol/g (25 °C/30 bar), whereas 4–9-2-m has a maximum capacity of 3.46 (25 °C/1 bar) and 5.42 mmol/g (0 °C/1 bar) and outstanding CO2/N2 selectivity (123 at 0.02 bar). The pressurized CO2 adsorption capacity is positively correlated with total pore volume. While under atmospheric pressure, the optimal adsorption site of biochar at 25 °C is ultramicroporous(0.5 nm) and oxygen-containing functional groups, and transforms into ultramicroporous(0.7 nm) and N-5 groups at 0 °C. The simulation results show that 0.5 nm is the pore size of CO2 adsorption from monolayer to bilayer, and both oxygen/nitrogen-containing groups could increase the CO2 adsorption capacity of biochar. This study provides guidance for the preparation of excellent carbon-based CO2 adsorbents according to application scenarios.

Decoupling the Ca release characteristics induced by O-containing functional groups during volatile-char interaction based on model compounds

Alkali metals and alkaline earth metals (AAEM) are important factors to be considered in coal gasification process, and understanding the release behavior of AAEM under the interaction of volatile-char is the key to realize efficient thermal conversion of coal. In this study, four typical O-containing functional groups (—COOH,—OH, CO,—OCH3) were used to react with coal char in a fixed-bed reactor, the reaction temperature was set up at 750，800，850，900 ℃ to survey the release characteristics of Ca by different oxygen functional groups during the interaction of volatile-char at different temperatures from a quantitative point of view. The result show that the Ca release rate of coal char is not high in the whole reaction temperature range, and the interaction of O-containing compounds-coal char at lower temperature will increase the O content (C—O and CO) of coal char, the content of Ca in interactive coal chars was higher than that of the coal char. At lower temperature, the order of compounds inhibiting Ca release ability is: C6H5CHO≈C6H5COOH > C10H8O2 > C6H5OCH3. In addition, it also seems that O-containing compounds (except C6H5COOH) can obviously promote the conversion of ammonium acetate-soluble Ca to water-soluble Ca during the interaction with char. As the temperature increases, the change trend of O-containing functional groups on the surface of sample after interaction is completely opposite to that at lower temperature, the O-containing model compounds undergo de-oxidation, cracking and polymerization in the effect of coal char and AAEM, causing the formation of polycyclic aromatic hydrocarbon on the surface of the char, which hinders the diffusion of Ca from the char to the gas phase. This work is good for enriching and developing the study on the release characteristics of alkali earth metals during the interaction of volatile-char, and provides a theoretical basis for the development of related industries.

Occurrence of Differences between Alkali and Alkaline Earth Metals (AAEMs), Including Sodium, Potassium, Calcium, and Magnesium, in the Maceral Groups of the Xiheishan Coal, Zhundong Coalfield, Xinjiang, China

This study investigated the differences and correlation between the occurrence characteristics of alkali and alkaline earth metals (AAEMs) among different maceral groups in high-alkali, high-inertinite coal, and provides scientific guidance for the co-separation of AAEMs and inertinite groups in Xinjiang coal. The total AAEMs of inertinite-enriched samples were significantly higher than those in raw coals and vitrinite-enriched samples. Five-step sequential extraction showed that Na mainly occurs as water-soluble sodium (Na-Water) in raw coal and inertinite-enriched samples, accounting for about 53% of the total content, while it exists as organic sodium (Na-NH4Cl and Na-EDTA) in vitrinite-enriched samples, accounting for about 52% of the total content. Ca and Mg are both mainly present in organic form (Ca/Mg-NH4Cl and Ca/Mg-EDTA) in all the samples, with slightly higher proportions present in vitrinite-enriched samples. The contents of K are low in all the samples, which exist in an insoluble state (K-I). Combined microscopy and SEM-EDS analyses have revealed that the localized enrichment of Na in raw coal and inertinite-enriched samples occurs in the inertinite cell cavity, which primarily exists as NaHCO3 combined with quartz crystals, with a maximum content of up to 5.85 wt%. In this study, although EDS spectra could not directly characterize organic Ca and Mg, dolomite and calcite minerals were repeatedly found in the inertinite cell cavity. Moreover, the contents of Ca and Mg in the vitrinite-enriched samples were significantly lower than those in the other samples, which suggests that Ca and Mg are enriched with the inertinite groups. The localized enrichment of AAEMs could not be detected in any of the vitrinite-enriched samples. In summary, though there are significant differences between the occurrence modes of AAEMs in different maceral groups of high-alkali coal, AAEMs have a strong affinity with inertinite, which may be due to the inertinite’s abundant pore structures.

Synergistic interactions between lignite and biomass during co-pyrolysis from volatile release, kinetics, and char structure

One of the most efficient techniques to achieve efficient utilization of both is coal and biomass co-pyrolysis. Despite a great deal of recent research on the co-pyrolysis process, it is still unknown how biomass affects the co-pyrolysis's synergistic effect and how volatiles interact. This study uses a thermogravimetric analyzer to examine the weight loss law of co-pyrolysis of wheat straw, rice straw, and bamboo powder with various amounts of Zhundong coal. According to the findings, there is a strong positive interaction, a mild positive interaction, and a negative interaction when three different types of biomass (wheat straw, rice straw, bamboo straw) are co-pyrolysis with Zhundong coal. The interaction between wheat straw and Zhundong coal is the strongest when the mass ratio of wheat straw to Zhundong coal is 6: 4. Using a thermogravimetric-infrared spectrometer, the changes in volatile functional groups during co-pyrolysis are investigated. It is discovered that adding wheat straw decreased the amount of CO2 produced by Zhundong coal pyrolysis. Regarding the mechanism of co-pyrolysis, the alkali and alkaline earth metals (AAEMs) on the surface of biochar catalyze the pyrolysis of Zhundong coal, while the “hydrogen donor” and “free radical donor” generated by biomass pyrolysis inhibited the cross-linking and polymerization of macromolecular volatiles produced by Zhundong coal pyrolysis. The activation energy of the mass ratio of wheat straw to Zhundong coal = 6: 4 sample is calculated by three model-free methods. The co-pyrolysis process's average activation energy is determined to be between 175.95 and 194.18 kJ/mol. Through scanning electron microscopy, it is found that the morphology of co-pyrolysis carbon is significantly different from that of single pyrolysis carbon. The porous structure of biochar promotes the secondary cracking of heavy volatiles produced by coal pyrolysis, while the cracking of volatiles further promotes the development of the pore structure of biochar.

Co-gasification of lignite and spent tea waste for the generation of hydrogen-rich syngas in a fluidized bed gasifier

The co-gasification of high moisture and high volatile content low-rank lignite (LG) coal and a common waste generated from the brewed tea leaves was studied in a fluidized bed gasification unit. Multiple experiments were conducted at different temperatures, ranging from 800 °C to 900 °C, at fixed operating parameters to elucidate the catalytic thermo-chemical impact on the gasifier performance parameters. The catalytic effect of alkali and alkaline earth metals (AAEMs), especially CaO, K2O, and Na2O present in the spent tea waste (STW) sample, on the product gas composition and performance parameters during the co-gasification experiments with LG was demonstrated. Mixed blends of LG and STW showed enhancement in the overall reactivity of the steam gasification runs, compared to the LG-only feed, primarily due to the change in the surface morphology, textures, and pore structures of the solid product ash samples, as identified with the electron spectroscopy analysis. Liquid and product samples were analyzed using characterization techniques such as Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) analytical techniques, along with the proximate, ultimate, and X-ray fluorescence (XRF) analysis of the gasification feed samples. An optimized blend ratio of 20 wt % of STW with LG sample enhanced the volumetric gas composition of H2 and CH4 gases from 52.03 % to 61.32 % and 3.98 %–5.45 % (on a dry-N2-free basis) with a relatively constant CO gas composition. It showed a reduced CO2 composition from 28.64 % to 18.25 % (on a dry-N2-free basis) for the gasification temperature of 900 °C. Even at the lower gasification temperatures of 800 °C and 850 °C with LG + STW feed, steam gasification experiments showed relatively comparable or superior performance to gasification experiments at 900 °C with LG-only feed. The present study indicated a holistic way to utilize the spent tea waste generated from millions of homes and commercial establishments in various parts of the world with potential application towards synergistic gasification process with other conventional carbon-source materials.

Catalytic pyrolysis of poplar sawdust pretreated with combined leaching and torrefaction over Fe–Ni/ZSM-5 for aromatic-rich bio-oil production

High oxygen content and alkali and alkaline earth metals (AAEMs) naturally present in biomass exhibit detrimental effects on biomass pyrolysis. Hence, effective pretreatment methods are essential for enriching the desired pyrolytic products (aromatics). In this study, poplar sawdust (PS) pretreated with a combination of acid leaching and torrefaction was catalytically pyrolyzed using Fe–Ni/ZSM-5 for enhanced aromatic production. The findings show that the coupled pretreatment effectively removed AAEMs while also lowering the H/C and O/C ratios. The combined pretreatment method increases the activation energy of the raw sample from 126.38 kJ mol−1 to 154.38–158.33 kJ mol−1. The enrichment of aromatics in bio-oils was significantly aided by the pretreatment process, with benzene, toluene, and xylene increasing from 82.24 mg g−1 of raw PS catalytic pyrolysis to 97.48–103.83 mg g−1 of the pretreated PS. This study demonstrates that combined pretreatments of biomass enhanced the quality of pyrolytic products, which could be a valuable framework for practical application.

Mechanisms for NOx emission control and ash deposition mitigation in sludge-coal blend combustion

This paper introduces the coupled treatment of alkali and alkaline earth metals (AAEMs)-rich coal with ferric sludge as a method to efficiently and economically control sludge NOx emissions and mitigate coal ash deposition through fuel interactions. We utilized a pilot-scale drop tube furnace to quantify NOx emissions and ash deposition, supported by spectral and energy dispersive analyses. The results demonstrated co-combustion controls NOx emissions by catalyzing the reaction between char and NO and the transformation into more stable N-containing functional groups. It also facilitates the formation of harmless N2 instead of NOx by enabling Ca/Fe-based minerals to react with protein and pyrrolic nitrogen. At 950 °C, blending 10% ferric sludge mitigated ash deposition, thanks to the capture and dilution effect of Si/Al/Fe-based minerals in ferric sludge. However, blending ferric sludge aggravated ash deposition of AAEMs-rich coal at 1250 °C, due to the formation of eutectics by Fe-based minerals and Ca/Na-based feldspars. Besides, the control of NOx was reduced at 1250 °C. Therefore, the co-combustion of AAEMs-rich coal with 10% ferric sludge at 950 °C exhibited excellent performance in both emission control and ash deposition mitigation. This study, grounded in the characteristics of minerals, provides a theoretical foundation for the efficient and economical in-situ control of NOx emissions and ash deposition. It advances the development of low-carbon, environmentally friendly technologies for coupled sludge and coal combustion.

Effects of alkali and alkaline earth metals on co-combustion of sewage sludge and coal slime: Combustion characteristics, interactions, and kinetics

The co-combustion of sewage sludge (SS) and coal slime (CS) is a preferred method for their resource utilization, however, alkali and alkaline earth metals (AAEMs) in SS may affect the co-combustion process. In this work, the co-combustion behavior of AAEMs-rich SS and CS was investigated in terms of combustion characteristics, interactions, and combustion kinetics using a thermogravimetric analyzer. Further, the role of AAEMs in co-combustion was evaluated by loading Ca, K, Na, and Mg individually after pickling. The results revealed that co-combustion compensated for the limitations of the individual combustion processes, with SS reducing ignition and burnout temperatures and CS improving the comprehensive combustion characterization. Principal component analysis (PCA) showed that the effect of CS on co-combustion was more significant compared to SS. Significant synergies were observed in the weight loss phase of fixed carbon in the blends with 40%, 50%, and 60% CS ratios, where the peak temperature of fixed carbon combustion was reduced by 9.8 °C, 12.6 °C, and 13.1 °C, respectively, compared to the theoretical values. The effects of AAEMs on combustion were as follows: all AAEMs promoted the precipitation of volatiles except Ca, which showed inhibition of light volatiles; AAEMs had a significant catalytic effect on fixed carbon combustion. The improvement effect of AAEMs on the comprehensive combustion characteristics during co-combustion was Na > K > Mg > Ca. The catalytic effect of Na on fixed carbon was strongest at a loading of 5%, leading to a decrease in the apparent activation energy of fixed carbon combustion by 22.2 kJ/mol and a change in reactor order from n = 1 to n = 1.2 during co-combustion. This work provides a better understanding of the role of AAEMs in SS-CS co-combustion.

Effects of SO2 and H2O on the ash deposition and NO emission during oxy-fuel combustion of high-alkali coal

The oxy-fuel combustion is promising to realize the large-scale CO2 capture and effective reduction of nitric oxides. The recirculation of flue gas in oxy-fuel combustion can lead to high concentrations of SO2 and H2O, which probably affects the ash deposition of high-alkali coal because SO2 and H2O are important for the transformation of alkali and alkaline earth metals (AAEMs). In the present work, the effects of SO2 and H2O in recycled flue gas on the ash deposition and NO emission during the oxy-fuel combustion of high-alkali coal were experimentally evaluated in a vertical two-stage furnace system. The conversion ratio of fuel-nitrogen to NO (CNO) and ash deposition efficiency were measured, and then the ash deposits were subjected to a couple of tests for further analyses. The experimental results show that SO2 helps to reduce the NO emission and its impact on ash deposition depends heavily on its concentration. In the case with modest SO2 addition, the sulfations of sodium and calcium are enhanced to some extent. Consequently, the amount of small sticky particles (NaCl and sodium aluminosilicates) that attached to large particles decreases, and the large particles mainly made of calcium aluminosilicates become smaller and less sticky. The newly generated Na2SO4 and CaSO4 are insufficient to overcome the inhibiting effects, thus the ash deposition efficiency decreases. Under the condition of excessive SO2 addition, the sulfations are further promoted. The small particles rich in Na2SO4 and CaSO4 are substantially more, which can not only serve as the initial ash layer on the heating surface, but also strengthen the stickiness of large particles by attaching to their surfaces. Therefore, the ash deposition efficiency increases·H2O can reduce the NO emission, while it aggravates the ash deposition because H2O enhances the sulfation.

Effect of Sequential Pre-treatment on the Thermal Behavior of Pretreated Palm Empty Fruit Bunch using Thermal Gravimetric Analyzer

Utilizing sequential pre-treatment of demineralization and torrefaction on biomass prior to pyrolysis has shown to be promising in enhancing the solid fuel feedstock properties. The aim of this study is to further investigate the suitable biomass feedstock for the pyrolysis process by monitoring the thermal degradation behaviors of different pre-treated palm empty fruit bunch (PEFB) prior to pyrolysis process. Thermal analyses of all samples were performed using a Mettler Toledo TGA at a heating rate of 20 °C·min−1 with nitrogen flow of 100 mL·min−1 from ambient temperature to 900 °C. The thermogravimetric analysis displayed that the torrefied demineralised palm empty fruit bunch (TDPEFB) has experienced major weight loss of 61.53% at its active degradation temperature. Meanwhile, torrefied palm empty fruit bunch (TPEFB) showed a lower amount of weight loss compared to TDPEFB since the presence of alkali and alkaline earth metal (AAEM) in TPEFB which inhibits the primary reaction, thus leading to the retention of mass in the biochar fraction. In comparison, the percent weight loss for untreated PEFB was recorded to be the lowest among the three samples which is about 33.9% during the active pyrolysis process. The results support the argument that the demineralization process has assisted primary reactions by the removal of AAEM. This in turn contribute to higher weight loss of sample as more volatile matters and cellulose content could be released during thermal degradation of the TDPEFB. Subsequently, the quality and quantity of bio-oil produced could be enhanced. This sequential pre-treatment was suggested to be an effective approach for upgrading the quality of solid fuel feedstock for further thermal conversion processes such as pyrolysis.

The effect of alkali and alkaline earth metals (AAEMs) on combustion and PM formation during oxy-fuel combustion of coal rich in AAEMs

This study focused on the effect of alkali and alkaline earth metals (AAEMs) on combustion and particulate matter (PM) formation during oxy-fuel combustion of coal rich in AAEMs. The combustion characteristics and PM formation were investigated using thermogravimetric analyzer and drop tube furnace, respectively. The results showed a catalytic role of AAEMs in coal combustion. Addition of AAEMs can decrease ignition temperature and burnout temperature and increase the comprehensive combustion index. The catalytic effect of alkali metals was stronger than alkaline earth metals. The optimal addition ratio of AAEMs was 3 wt%. Pretreatment, such as water or acid washing, effectively reduced the formation of PM0.4. Increasing furnace temperature or O2 concentration can increase particle temperature during oxy-fuel combustion. Due to Na's higher volatility compared to Mg and Ca, increasing particle temperature cannot promote the vaporization of Na, but can enhance the reactions between Na-containing precursors and coarse particles. Thus, the content of Na in PM0.4 decreased. However, increasing particle temperature can promote the reduction reactions of Ca and Mg oxides, which was the primary reason why a higher furnace temperature or O2 concentration resulted in increased PM0.4 during oxy-fuel combustion of AAEMs-rich coal.

Investigation of Ash Deposition Characteristics in Full-Scale Circulating Fluidized Bed Boiler Burning Zhundong Coal

ABSTRACT Due to the high content of alkali and alkaline earth metals (AAEMs) in Zhundong coal, serious ash-related problems such as slagging and fouling occurred in the process of utilization, which has attracted wide attention. In this work, the ash deposition characteristics in a new type circulating fluidized bed boiler burning Zhundong coal was studied. The effect of steam cooled flue on alleviating slagging problems was evaluated, and the influence of flue gas temperature and wall temperature on ash deposition characteristics were studied. The results showed that the mass of ash deposition and the concentration of submicron particles decrease gradually along the direction of flue gas flow in the steam cooled flue. The deposited ash changed from tightly bound to wall to loosely deposited, which indicated that the arrangement of the steam cooled flue greatly alleviated the slagging problems. Compared with flue gas temperature, the wall temperature had a greater impact on ash deposition characteristics. Mineral elements such as Na, S, Fe and Mg were more likely to enrich on the high temperature wall, while the Ca showed the opposite trend. On the low temperature wall, Na existed in the form of Na2SO4 and Na2Si2O5, while on the high temperature wall, the direct condensation of alkali metal vapor was prevented and the thermophoresis disappeared, so Na mainly existed in the form of Na2Si2O5.

Impact of pretreatment with photocatalysis sequential coupling Fenton oxidation on physicochemical properties, pyrolysis behaviors, and product distribution of walnut shell

Naturally occurring alkali and alkaline earth metals (AAEMs) in biomass can adversely affect its pyrolysis behavior and product distribution and contribute to ash deposition in boilers. To address these challenges, we proposed a new idea of photocatalysis sequential coupling Fenton oxidation for biomass pretreatment. Our findings revealed that sequential pretreatment has the optimal moderating effects on biomass relative to individual photocatalysis and Fenton oxidation. The lignin and AAEMs in biomass were effectively reduced via sequential pretreatment, which was accompanied by cellulose content increased by 80.78% relative to untreated. Also, the slagging/fouling inclinations of biomass were successfully alleviated, and the pyrolysis performance was effectively improved. The kinetic parameters obtained based on the Coats-Redfern method can characterize the pyrolysis behavior well. During fast pyrolysis, sequential pretreatment caused the productivity of bio-oil was increased by 30.14% relative to untreated. In particular, the productivity of levoglucosan in bio-oil was increased by 364.71%. This study presented a novel and effective pretreatment strategy to improve the pyrolysis behavior and product distribution of biomass and alleviate ash deposition problems in boilers.

Effects of inherent AAEMs on catalytic gasification of biomass with large particle size under oxygen-steam atmosphere

Oxygen-steam gasification of biomass is a promising technology because of its ability to improve syngas quality and reduce energy consumption. In this study, a fixed-bed reactor is employed to assess the effects of inherent alkali and alkaline earth metals (AAEMs) on the catalytic gasification of candlenut wood with large particle size under the oxygen-steam atmosphere. Two grain directions, radial and axial, are considered for candlenut wood. Various characterization techniques, SEM, X-ray CT, BET, and FTIR, are employed to analyze biochar samples. GC-MS and GC are determined to tar and syngas respectively. The results show that char yield from biomass with axial grain is higher. Acid-washing removes alkali metals (K and Na) better from biomass with axial grain than radial grain, and vice versa for alkaline earth metals (Ca and Mg). In terms of the gasified chars derived from acid-washed biomass, AAEMs content gradually decreases along the end surface and radial direction, which could also be observed from the 3D reconstruction of X-ray CT images. In all samples, micropores (0–10 µm) dominate and are distributed along the grain direction. In general, pores of 20–30 µm and above 30 µm comprise a minor proportion. Inherent AAEMs facilitate an augmentation in char yield as well as BET and total pore volume of gasified char. AAEMs and grain direction have a slight effect on functional groups of gasified chars. Certain organic matter species and content in tar are remarkably affected by the grain direction, since the discrepancies of pore structure and specific surface area. Acid-washing pretreatment augments the content and organic species of M2-M4 compounds (containing 2–4 benzene rings) in the tar. K and Na significantly boost the char steam gasification, water-gas shift, and steam-tars reforming reactions. A decrement in concentrations of H2 (14.49% and 13.35%), CH4 (0.51% and 0.89%), and CO2 (2.32% and 1.37%) in syngas derived from acid-washed samples are acquired, respectively, compared to that of biomass samples with radial and axial grains. However, a reduction of 4.09% and 1.53% in syngas calorific value could be obtained. The CnHx volume fraction is significantly affected by grain direction and AAEMs, with axial grain yielding a higher volume fraction of C2H4 (49.07%), C2H2 (71.29%), and C3H8 (127.36%) from acid-washed sample than that of radial grain.

Effects of various pretreatments on fast pyrolysis of biomass to bio-oil: A case study of levoglucosan

Levoglucosan (LG), a valuable chemical derived from carbohydrates, is challenging to obtain with high yield directly from raw biomass. In this study, pyrolysis of a lignocellulosic biomass to LG was studied with various pretreatment methods, including acid, alkali, and torrefaction pretreatments. The results indicated that the hydrochloric acid washing effectively promoted the production of LG when the concentration of HCl was lower than 0.5 mol/L, mainly caused by the improved crystallinity of the cellulose fraction and the removal of alkali and alkaline earth metals (AAEMs). When 4% of NaOH solution was employed for the alkali pretreatment, the relative content of LG significantly increased from 3.07 to 73.59 with the temperature ranging from 130 to 170 ℃, owing to the effective removal of lignin and hemicellulose fractions. Biomass torrefaction at temperature lower than 250 ℃ slightly promoted LG production, but it inhibited the formation of LG when the temperature reached 300 ℃.

Valorization of coconut and banana wastes with petcoke and coal via steam gasification in a fluidized bed reactor

Steam gasification experiments were conducted with coal and petcoke in conjunction with potentially renewable biomass substances, namely coconut shell, coconut husk, and banana peduncle, which are usually considered waste materials. The gasification performance in a bench-scale externally heated fluidized bed gasifier was evaluated based on the product syngas quality and the detailed characterization of feed and product samples using X-ray fluorescence (XRF), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy analysis. This work performed experiments at relatively constant operating parameters: solid feed rate, steam/O2 ratio, feed particle size, and gasification reactor temperature. Biomass waste resources showed an augmentation in the syngas product quality for both the coal and petcoke samples, especially in cold gas efficiency (CGE) and carbon conversion efficiency (CCE). A maximum increase in CCE from 44.3 % to 72 % for the coal sample and from 19.3 % to 36.0 % for the petcoke sample was witnessed, whereas for the CGE, a rise of 35.8 %–91.7 % for the coal and 44.3 %–59.8 % for the petcoke with 80/20 blended biomass waste samples, was observed compared to the coal and petcoke only samples. The maximum hydrogen product gas yield between 53 and 73.7 vol % and combustible gas yields between 62.2 and 86.7 vol % were obtained on a nitrogen gas-free basis during the experiments. The solid residues of different gasification experiments were characterized and analyzed by scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) and field emission-scanning electron microscopy (FE-SEM) analytical techniques to elucidate the high yield of energy-intensive gases. FTIR analysis was performed on all the liquid product samples obtained during the gasification experiments. The presence of alkali and alkaline earth metals (AAEMs) in biomass wastes highlighted the catalytic effect of these elements during the gasification experiments. The current work provides an opportunity to reduce carbon footprints with effective and efficient utilization of conventional energy feedstocks in conjunction with other waste substrates.

Occurrence Modes of AAEMs (Na+ and Ca2+) and the Effect on the Molecular Structures of Zhundong Coal via Quantum Chemistry.

Zhundong coal is known for its high content of alkali and alkaline earth metals (AAEMs), which greatly influences coal processing and utilization. To reveal the occurrence modes and the effect of AAEM ions on the molecular structures of Zhundong coal, the previously constructed molecular structure models of vitrinite-rich and inertinite-rich Zhundong coal (ZD-V and ZD-I) were selected to simulate using quantum chemical methods. By focusing on Na+ and Ca2+, the adsorption capacity at different adsorption sites was investigated based on the density functional theory (DFT), and the effects of adsorption of Na+ and Ca2+ on nearby atomic charges, chemical bonds, and molecular orbitals were investigated. Results show that compared with ZD-I, ZD-V contains a more negative electrostatic potential (ESP) distribution and lower bond order, indicating that vitrinite contains more adsorption sites for AAEM ions and exhibits stronger chemical reactivity. Na+ and Ca2+ are easily adsorbed to the most negative ESP with the optimal adsorption site near the carbonyl group (C=O). Compared with adsorbed Na+, Ca2+ has a smaller adsorption distance from the molecule and a higher adsorption energy. Ca2+ can transfer more charge than Na+ and has more affinity with the coal molecule. Ca2+ at all adsorption sites is bound to organic molecules by chemisorption, which also reveals the reason for the low water-soluble Ca content in coal at the molecular level. Adsorption of AAEM ions has a more significant effect on the chemical bond of oxygen-containing functional groups near AAEM ions compared to the overall molecular fragments, which makes the nearby chemical bonds (C-O/C=O) decrease in bond order and increase in bond length. Ca2+ makes the nearby chemical bonds more prone to break than Na+. Additionally, Ca2+ has a more significant impact on the energy gaps (ΔEgap) compared to Na+. Adsorption of Ca2+ near the carbonyl and carboxyl groups leads to a significant decrease in ΔEgap, indicating an enhanced chemical reactivity of coal molecular fragments.

Correlation between Flow Temperature and Average Molar Ionic Potential of Ash during Gasification of Coal and Phosphorus-Rich Biomass

The co-gasification of biomass and coal is helpful for achieving the clean and efficient utilization of phosphorus-rich biomass. A large number of alkali and alkaline earth metals (AAEMs) present in the ash system of coal (or biomass) cause varying degrees of ash, slagging, and corrosion problems in the entrained flow gasifier. Meanwhile, phosphorus is present in the slag in the form of PO43−, which has a strong affinity for AAEMs (especially for Ca2+) to produce minerals dominated by calcium phosphates or alkaline Ca-phosphate, effectively mitigating the aforementioned problems. To investigate the changing behavior of the slag flow temperature (FT) under different CaO/P2O5 ratios, 72 synthetic ashes with varying CaO/P2O5 ratios at different Si/Al contents and compositions were prepared, and their ash fusion temperatures were tested. The effects of different CaO/P2O5 ratios on the FT were analyzed using FactSage thermodynamic simulation. A model for predicting slag FT at different CaO/P2O5 ratios was constructed on the basis of the average molar ionic potential (Ia) method and used to predict data reported from 19 mixed ashes in the literature. The results showed that Ia and FT gradually increased with a decreasing CaO/P2O5 ratio, and the main mineral types shifted from anorthite → mullite → berlinite, which reasonably explained the decrease in ash fusion temperatures in the mixed ash. The established model showed good adaptability to the prediction of 19 actual coal ash FTs in the literature; the deviation of the prediction was in the range of 40 °C. The model proposed between FT and Ia based on the different CaO/P2O5 ratios can be used to predict the low-rank coal and phosphorus-rich biomass and their mixed ashes.